1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, a method for producing the electrophotographic photosensitive member, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
An example of electrophotographic photosensitive members installed in process cartridges and electrophotographic apparatuses is an electrophotographic photosensitive member including an organic photoconductive substance (i.e., charge generating substance). Generally, an electrophotographic photosensitive member includes a support and a photosensitive layer, which is constituted by a charge generation layer and a charge transportation layer, formed on the support. An undercoat layer is interposed between the support and the photosensitive layer in order to suppress injection of charge from the support into the photosensitive layer and thereby suppress occurrence of image defects such as fogging.
Recently, a charge generating substance having high sensitivity has been employed. However, the higher the sensitivity of the charge generating substance, the stronger the tendency of charge to remain at the interface between the photosensitive layer and the undercoat layer due to an increase in the amount of charge generated. In the case where images are formed repeatedly for a long period of time in this state, a large change in the surface potential of the electrophotographic photosensitive member may occur, which is likely to cause image defects such as ghost images. In Japanese Patent Laid-Open No. 2007-148357, a technique in which titanium oxide particles are added to the undercoat layer in order to suppress the potential change is described.
Recently, there have been demands for an increase in the print speed of electrophotographic apparatuses and a decrease in the amount of maintenance required, and therefore there has also been a demand for enhancement of the durability of an electrophotographic photosensitive member. Accordingly, there has been proposed a technique in which a curable resin is added to the surface layer of an electrophotographic photosensitive member in order to enhance the mechanical durability (i.e., wear resistance) of the electrophotographic photosensitive member. In Japanese Patent Laid-Open No. 2000-66425, a surface layer including a cured product of a charge transporting compound having two or more polymerizable functional groups per molecule is described. In Japanese Patent Laid-Open No. 2004-302450, a surface layer including a cured product formed by irradiating a composition including a charge transporting compound having one polymerizable functional group, a radical-polymerizable monomer which has three or more polymerizable functional groups and which does not have hole transportability, and a photopolymerization initiator with ultraviolet radiation is described.
However, as a result of studies conducted by the inventors of the present invention, the following problem was found in an electrophotographic photosensitive member constituted by an undercoat layer including titanium oxide and a surface layer including a cured product formed by irradiating, with ultraviolet radiation, a composition including a compound having a polymerizable functional group and a photopolymerization initiator. Specifically, there were cases where black-dot-like image defects (hereinafter, referred to as “black dots”) were likely to occur.